1. Field of the Invention
The present invention relates to a dielectric antenna for use in portable terminals and in radio communication devices.
2. Description of Related Art
Japanese Patent Application Laid-Open (kokai) No. H10-98322 discloses a dielectric antenna of the above-mentioned type. In that dielectric antenna, a radiation electrode serving as an antenna element is provided on a first main surface of a plate-shape dielectric substrate, whereas a ground electrode is provided over the entirety of a second main surface of the dielectric substrate. The radiation electrode is formed so as to be smaller than the ground electrode. A coaxial feeder is disposed in such a manner that the center conductor of the coaxial feeder passes through the dielectric substrate from the second main surface to the first main surface, and the outer conductor of the coaxial feeder is connected to the ground electrode.
Japanese Patent Application Laid-Open (kokai) No. 2000-261235 discloses a microstrip antenna configured so as to use a tri-plate line as a feed line. In that microstrip antenna, a pair of ground conductors, are formed on outer surfaces of two feed dielectric layers stacked one on the other, and a center conductor is formed between the pair of ground conductors. Further, a third dielectric layer is stacked on one of the pair of ground conductors, and a radiation electrode is formed on an outer surface of the third dielectric layer. A shield member connects the pair of ground conductors together to thereby provide electrical shielding between the space inside the shield member and the space outside the shield member.
Japanese Patent No. 2833802 discloses a microstrip antenna configured in such a manner that a radiation conductor is provided on a first main surface of a plate-shape dielectric substrate so as to be located at a substantially central portion of the first main surface, and a first ground conductor is provided over the entirety of a second main surface of the dielectric substrate. In that microstrip antenna, a second ground conductor for reducing electric fields between the radiation conductor and the first ground conductor is provided on a peripheral portion of the plate-shape dielectric substrate, and the distance between the radiation conductor and the first ground conductor is shortened, whereby electric fields formed in the air between a peripheral edge portion of the radiation conductor and the ground conductor are reduced.
Dielectric antennas of the above-described types are conventionally incorporated into portable terminals and radio communication devices. However, portable terminals and radio-communication devices have increasingly been made smaller in size, i.e., miniaturized, and reduced in weight, in order to make the use thereof more convenient. With the miniaturization of the overall devices associated therewith, there has been an increasing demand for miniaturization of dielectric antennas in order to enable installation of a dielectric antenna within a limited space. However, even when a miniaturized dielectric antenna is employed, the dielectric antenna is, in practice, mounted on a printed circuit board so as to be located adjacent to other electronic circuit elements and metallic parts. As a consequence, the mounted dielectric antenna is influenced by electronic circuit elements and metallic parts surrounding the antenna, with the result that the electrical characteristics of the antenna are unstable. One conceivable technique for solving this problem is to provide a shield member around the dielectric antenna so as to reduce the destabilizing influences. However, the provision of such a shield member is undesirable because of the limited installation space available and the resultant increase in the number of parts required, thus adding to the overall cost and making miniaturization of the overall device more difficult.
In view of the foregoing, an object of the present invention is to provide a dielectric antenna which is not influenced by surrounding metallic parts and electronic parts and, therefore, has stable electric characteristics.
To achieve the foregoing and other objects, there is provided, in accordance with one aspect of the present invention, a dielectric antenna comprising: a plate-shaped dielectric substrate having first and second main surfaces; a radiation electrode provided on the first main surface of the dielectric substrate so as to cover the first main face except for, i.e., apart from, a peripheral portion thereof; a ground electrode formed on the entirety of the second main surface of the dielectric substrate; a feed electrode extending through the dielectric substrate from the first main surface to the second main surface, a feed point of the feed electrode being electrically connected to the radiation electrode; and a plurality of through-hole electrodes formed in a peripheral portion of the dielectric substrate so as to surround the radiation electrode, the through-hole electrodes being connected to the ground electrode.
The above-described configuration enables the antenna itself to perform a shielding function, and thereby eliminates the necessity of incorporating a separate shield member into the device or equipment into which the antenna is mounted or incorporated. Therefore, the configuration of the present invention is advantageous from the viewpoints of both cost and space savings. Further, the antenna is unlikely to be influenced by electronic parts and metallic parts disposed around the antenna, so that adverse influences on the electrical characteristics of the antenna are mitigated so as to thereby stabilize the electrical characteristics of the antenna.
Preferably, the dielectric substrate is of a substantially rectangular shape as viewed from the first main surface, and the plurality of through-hole electrodes include through-hole electrodes formed along each side of the rectangular shaped substrate at substantially constant intervals, i.e., with substantially constant spacing between the through-hole electrodes.
Preferably, one corner portion of the dielectric substrate is chamfered, the radiation electrode is of a substantially rectangular shape corresponding to the rectangular shape of the dielectric substrate, and a first corner portion of the radiation electrode corresponding to the chamfered corner portion of the dielectric substrate, and a second corner portion of the radiation electrode diagonally opposite the first corner portion, are each cut at an angle equal to the chamfer angle of the chamfered corner portion of the dielectric substrate.
Preferably, the feed electrode is provided at a position offset from a center of the dielectric substrate as viewed from the first main surface.
In accordance with a further aspect of the present invention, there is provided a dielectric antenna comprising: a plate-shaped dielectric substrate having first and second main surfaces; a radiation electrode provided on the first main surface of the dielectric substrate so as to cover the first main face except for a peripheral portion thereof; a ground electrode formed on the entirety of the second main surface of the dielectric substrate; a feed electrode extending through the dielectric substrate from the first main surface to the second main surface, a feed point of the feed electrode being electrically connected to the radiation electrode; and a shield electrode formed on a side surface of the dielectric substrate and connected to the ground electrode.
The above-described configuration also enables the antenna itself to perform a shielding function, and to thereby eliminate the necessity of incorporating a separate shield member into the device or equipment in which the antenna is mounted. Therefore, this configuration of the present invention is also advantageous from the viewpoints of both cost and space savings. Further, as with the first embodiment, the antenna is unlikely to be influenced by electronic parts and metallic parts disposed near or around the antenna, so that any adverse effects on the electrical characteristics of the antenna can be mitigated so as to stabilize the electrical characteristics of the antenna.
Preferably, the dielectric substrate is of a substantially rectangular shape as viewed from the first main surface, and a substantially rectangular shield electrode is formed on each of four side surfaces of the dielectric substrate. In this implementation, the shield electrode may be connected to the ground electrode through one side of the shield electrode, and the remaining sides of the shield electrode may be spaced or separated from corresponding sides of the corresponding side surface. Alternatively, the shield electrode may be connected to the ground electrode through one side of the shield electrode, and the remaining sides of the shield electrode extend to corresponding sides of the corresponding side surface of the dielectric substrate, so that the shield electrodes on the four side surfaces are connected with one another in the circumferential direction, i.e., are laterally connected together.
Preferably, in this embodiment as well, one corner portion of the dielectric substrate is chamfered, the radiation electrode is of a substantially rectangular shape corresponding to the rectangular shape of the dielectric substrate, and a first corner portion of the radiation electrode corresponding to the chamfered corner portion of the dielectric substrate, and a second corner portion of the radiation electrode diagonally opposite the first corner portion, are each cut at an angle equal to the chamfer angle of the chamfered corner portion of the dielectric substrate.
Preferably, in this embodiment as well, the feed electrode is provided at a position offset from a center of the dielectric substrate as viewed from the first main surface.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.